Development of “magnetic nano-beads” has been promoted as one of promising medical materials for use in next-generation medical techniques. The magnetic nano-beads (hereinafter, also denoted as magnetic microparticles) are nano-level size microparticles of ferrite (solid solution of Fe3O4 and γ-Fe2O3). Recently, there has been developed a technique of synthesizing them under mild conditions of 4 to 25° C. in the range of a neutral pH, as described in JP-A No. 2002-128523 (hereinafter, the term, JP-A refers to Japanese Patent Application Publication). Magnetic nano-beads for medical use have been proposed, in which drugs or physiologically active materials are allowed to be fixed onto (attached to or included in) the magnetic microparticles covered with dextran, lipid, liposome, polymer or the like, as described in JP-A Nos. 2002-128523 and 9-110722. As application of such magnetic microparticles in the medical field are proposed applications to contrast medium material used for MRI diagnosis or a medicine-transporting carrier, and thermotherapy employing heat generation due to hysteresis loss of magnetic microparticles in the high frequency magnetic field; there was further proposed concurrent performance of diagnosis and therapy of cancer by the combination of both of the foregoing, as described in “BIO INDUSTRY” vol. 21, No. 8, page 48-54 (2004).
Thermotherapy for cancer (Hyperthermia) has been proposed for several decades and is one of the cancer therapies studied. The principle of therapy employs a property of cancer cells being weaker to heat than normal cells, thereby giving therapy with artificially maintaining a high temperature environment. Thermotherapy for cancer is a non-invasive treatment as compared to surgical removal operation which is generally conducted for cancer therapy. Comparing to chemotherapy or radiotherapy which often results in adverse effects, it is selective and its adverse effect becomes lower. Thus, it is a treatment which makes preservation of organs feasible and enhances the patient's quality of life. It is therefore a treatment suitable for an early cancer, or aged persons or infants who are intolerable to operative invasion or adverse effects. Conventional thermotherapy has employed techniques such as induction heating or focused ultrasonic heating and a recent alternant magnetic field heating using a ferrite type MRI contrast medium, and each of these therapies has merits and demerits. Accordingly, there is studied the possibility of using the above-described ferrite type particles as a novel heat-generating element in the alternating magnetic field, as described in “BIO INDUSTRY” vol. 21, No. 8, page 48-54 (2004).
Feasibility of putting employment of magnetic microparticles into practice in the medical field relies on capability of maintaining a physiologically active material, a treatment drug or the like within the beads or capability of its selective delivery to an intended site (targeting capability). In this regard, the magnetic vesicular particles which have been proposed so far, still leave room for improvement. In enclosure of magnetic microparticles within liposome vesicles, various problems relating preparation of the liposome, for example, residue of organic solvents and stability of a liposome structure retard its practical use.